1. Technical Field
The present invention relates to optical elements that emit laser light and methods for manufacturing the same.
2. Related Art
A surface-emitting type semiconductor laser is one type of optical elements that emit laser light. The surface-emitting type semiconductor laser is provided with a resonator formed in a direction orthogonal to a surface of the substrate, and emits laser light from an upper surface of the resonator. A surface-emitting type semiconductor laser has a smaller device volume compared to an ordinary edge-emitting type semiconductor laser, such that the electrostatic breakdown voltage of the device itself is low, and in particular, the device has a low dielectric breakdown withstanding property against reverse bias voltages. For this reason, the device may be destroyed by static electricity caused by a machine or an operator during a mounting process. To solve this problem, for example, U.S. Pat. No. 6,185,240 describes a technology in which a surface-emitting type semiconductor laser and a rectification diode that circulates a current only when a reverse bias voltage is applied to the surface-emitting type semiconductor laser are connected in parallel with each other and formed on a substrate.
FIG. 16A is a schematic cross-sectional view of an exemplary structure of an optical element formed from a surface-emitting type semiconductor laser and a rectification diode. As shown in the figure, a first n-type semiconductor layer 31 (a distributed reflection type multilayer mirror composed of n-type semiconductor) is formed on a substrate 30, and an i-type semiconductor layer 32 and a first electrode 33 are formed on the first n-type semiconductor layer 31. Columnar first p-type semiconductor layer 34 and second p-type semiconductor layer 35 (distributed reflection type multilayer mirrors composed of p-type semiconductor) are formed, separated from each other, on the i-type semiconductor layer 32, and an insulation layer 36 is formed in a manner to cover side surfaces of the first p-type semiconductor layer 34 and the second p-type semiconductor layer 35. A second n-type semiconductor layer 37 and a second electrode 38 are formed on the second p-type semiconductor layer 35. A third electrode 39 defining an opening section 34a is formed on the first p-type semiconductor layer 34, the insulation layer 36 covering the side surface of the first p-type semiconductor layer 34, and the second n-type semiconductor layer 37, whereby the first p-type semiconductor layer 34 and the second n-type semiconductor layer 37 are conductively connected with each other. Further, a fourth electrode 40 is formed to conductively connect the first electrode 33 and the second electrode 38 with each other.
The first n-type semiconductor layer 31, the i-type semiconductor layer 32 and the first p-type semiconductor layer 34 compose a surface-emitting type semiconductor laser V, wherein laser light is emitted from the opening section 34a. Also, the second p-type semiconductor layer 35 and the second n-type semiconductor layer 37 compose a rectification diode E. In other words, the optical element has, as shown in FIG. 16B, the surface-emitting type semiconductor laser V and the rectification diode E connected in parallel with each other, wherein a current flows through the rectification diode E only when a reverse bias voltage is applied to the surface-emitting type semiconductor laser V.
Because the surface-emitting type semiconductor laser V and the rectification diode E are formed in columnar structures disposed separated from each other in the manner described above, side surfaces of the columnar sections are covered by the insulation layer 36 to suppress step differences where the electrodes are formed as much as possible. As a material of the insulation layer 36, a resin material such as polyimide and the like is generally used, but the coefficients of the resin material and the semiconductor material are greatly different from each other. More concretely, when heated, the insulation layer 36 contracts in a greater amount than the columnar sections that are composed of the semiconductor material. Accordingly, if a heating step is conducted in the process for manufacturing an optical element, or the temperature of the optical element that has been finished as a product rises during its use, the insulation layer 36 may be exfoliated from the columnar sections, and the electrodes may be disconnected at interfaces between the insulation layer 36 and the columnar sections. The disconnection of the electrodes that may occur with a temperature increase would cause a lowered yield in the manufacturing process, and a lowered reliability in the product.